Semi-crystalline polyolefins such as polypropylene have gained wide commercial acceptance and usage in numerous applications because of the relatively low cost of the polymers and the desirable properties they exhibit. These properties include good impact resistance, good heat stability and high chemical resistance. In general, polypropylene polymers, particularly propylene homopolymers, have a disadvantage of being brittle with low impact resistance, especially at low temperatures. To address these issues, manufacturers have incorporated another material rubber, which forms a dispersed phase within the polypropylene matrix. These two-phase materials are referred to as impact copolymers or ICPs.
Polyolefins can be also used in the form of foams. Expanded polypropylene (EPP) is a foam form of polypropylene. Foamed polypropylene has very good impact characteristics due to its relatively low stiffness. However, the production of polypropylene foams are limited because of its low melt strength and melt elasticity, and the associated high cost for manufacturing.